This invention relates generally to delivering a continuous positive air pressure, and more particularly to an improved apparatus for delivering a continuous positive air pressure to an infant.
The medical profession has used positive pressure therapy to treat ventilatory insufficiency since 1936. Continuous distending pressure ("CDP") is the maintenance of an increase transpulmonary pressure during the expiratory phase of respiration. CDP is a general term used to denote continuous positive airway pressure ("CPAP") when the patient is breathing spontaneously or positive end-expiratory pressure ("PEEP") when the patient is assisted on ventilation. CDP systems were initially used primarily for adult respiratory problems. By 1971, medical reports documented the use of CPAP in spontaneously breathing newborn infants with idiopathic respiratory distress syndrome.
The benefits of an increased alveolar pressure for use on infants with respiratory distress syndrome have been recognized for a number of years. The use of CPAP has also been extended into the treatment of neonatal problems other than respiratory distress syndrome, such as apnea of prematurity, patent ductus arteriosus, meconium aspiration syndrome and post-surgical cases. Several methods of delivering CPAP from a positive air flow source to infants have been used, including endotracheal tube, head box, face chamber, face mask, and nasal/nasopharyngeal prongs.
CPAP keeps lungs expanded on exhalation while an infant does its own breathing. CPAP keeps the lungs from collapsing on exhalation and allows a more efficient exchange of oxygen and carbon dioxide to occur. CPAP reduces the effort required to breathe and breathing is typically more regular with infants on a CPAP system.
Many devices and systems are currently available to provide a CPAP source. These devices and systems function on substantially the same principle and typically employ a continuous gas flow, a reservoir bag, a valve to produce above ambient expiratory pressure, and a humidification device. The amount of CPAP may be varied by changing the amount of gas flowing into the system or by changing the amount of obstruction to outflow. Gas flow is regulated through a flow meter. Flow through the circuit is a function of the resistance to flow determined by the diameter and length of the associated tubing.
The endotracheal tube was the original system used to deliver CPAP in infants. The endotracheal tube allows the use of low flows while maintaining high pressure with minimum leakage. However, the endotracheal tube causes acute airway trauma. The endotracheal tube can becomes kinked or blocked during or following insertion. Tracheal stenosis, scaring and severe irritation are possible by the use of such system.
The head chamber is a non-invasive, closed system that permits the use of low flows. The head chamber is not effective for small infants weighing less than 1,500 grams. With the head chamber, there is a delay in access to the face and mouth. The infant is inaccessible and movement is limited. This modality produces high noise levels and has been associated with certain neck problems for infants using the head chamber.
The face chamber has similar problems to the head chamber. During application, the patient must be in a cradle for positioning purposes. The face chamber has not gained wide acceptance in the United States.
The face mask is a simple and inexpensive option for delivering CPAP to an infant. The mask must be securely placed and must cover both nose and mouth. Pressure buildup and carbon dioxide retention are possible problems which may occur with use of the face mask for CPAP. The face mask may produce severe gastric distension and typically requires an orogastric for decompression.
Nasal prongs and nasopharyngeal prongs are another system for applying CPAP. Nasal prongs are easy to apply and avoid the complication of endotracheal intubation. The current nasal prong designs are rigid structures which may cause trauma to the infant's nasal septum and turbinotes. When used with infants, crying is usually excessive and the infant loses pressure and inhales room air. The current nasal prongs are bulky and typically must be secured in a fixed position above the infant's head. The infant is required to lie on its back when connected to the system to assure proper operation of the nasal prongs.
Although there are may benefits to CPAP, there are some possible adverse affects, such as harmful effects on cardiac output and intracranial pressure. Such effects may be avoided by careful monitoring of distending pressure. Pulmonary air leaks and over distention of the lungs are also potential complications. Nasal CPAP is one of the least dangerous methods for applying CPAP. However, doctors and other hospital staff employees have found the present methods of applying CPAP either difficult to work with or highly uncomfortable for infants. Hospitals have a need for a new method of delivering CPAP to infants with respiratory problems.